Three-element electron discharge tube

ABSTRACT

In a high-vacuum electron tube, an elongated cylindrical control electrode is surrounded by an anode electrode including a plurality of segmental elongated partial anode surfaces extending parallel to and concentric with the axis of said control electrode and a plurality of incandescent cathode wires are disposed also parallel to said axis and each within the space intervening between adjacent anode surfaces. A magnetic field extending in a direction parallel to said axis within the space enclosed by said control electrode and said anode surfaces acts to deflect the electron streams emitted by said cathodes towards the adjacent anode surfaces and to thereby reduce the number of electrons reaching the control electrode. This in turn reduces the power necessary to drive the tube, in particular for tubes operated at a positive control potential (class-C operation). In order to achieve a desired amplification factor of the tube, individual shielding means interposed between each of the cathodes and the adjoining anode surfaces project into the space between the latter and the control electrode to an extent such as to cause, with the current flow through the tube being equal to zero, the electric field strength at said cathodes resulting from unity voltage upon the control electrode to be a predetermined multiple of the electric field strength at said cathodes resulting from unit voltage upon the anode, respectively.   D R A W I N G

United States Patent [72] Inventor Alexander Rusterholz Zurich, Switzerland [21] AppLNo. 712,451 {22] Filed Mar. 12,1968 [45] Patented Feb-9,1971 [73] Assignee Patelhold Patentverwertungs and Electro- HoldingA.G. Glarus, Switzerland [32] Priority Mar.l5, 1967 3 3 Switzerland [31] 3725 [54] THREE-ELEMENT ELECTRON DISCHARGE TUBE 9 Claims, 4 Drawing Figs.

[52] U.S.Cl 313/299, 3l3/302,3l3/84,313/304 [51] Int.Cl H0ljl/46, H0lj2l/l0 [50] FieldofSearch 313/299, 103, 302, 304, 278, 83, 84, 75

[56] References Cited UNITED STATES PATENTS 2,204,306 6/1940 Harris 313/299X 2,217,774 10/1940 Skellett.. 313/299X 2,636,142 4/1953 Garner... 3l3/304X 2,705,294 3/1955 Shrader 313/299X 2,727,177 12/1955 Daileyetal 3l3/299X 2,844,752 7/1958 Hoover 313/304X FOREIGN PATENTS 5/1949 France Primary Examiner-John W. Huckert Assistant Examiner-Andrew J. James Atmrneyl(arl Rath ABSTRACT: In a high-vacuum electron tube, an elongated cylindrical control electrode is surrounded by an anode electrode including a plurality of segmental elongated partial anode surfaces extending parallel to and concentric with the axis of said control electrode and a plurality of incandescent cathode wires are disposed also parallel to said axis and each within the space intervening between adjacent anode surfaces. A magnetic field extending in a direction parallel to said axis within the space enclosed by said control electrode and said anode surfaces acts to deflect the electron streams emitted by said cathodes towards the adjacent anode surfaces and to thereby reduce the number of electrons reaching the control electrode. This in turn reduces the power necessary to drive the tube, in particular for tubes operated at a positive control potential (class-C operation). In order to achieve a desired amplification factor of the tube, individual shielding means interposed between each of the cathodes and the adjoining anode surfaces project into the space between the latter and the control electrode to an extent such as to cause, with the current flow through the tube being equal to zero, the electric field strength at said cathodes resulting from unity voltage upon the control electrode to be a predetermined multiple of the electric field strength at said cathodes resulting from unit voltage upon the anode, respectively.

PATENTED FEB 91971 3,562,576

SHEET 2 OF 2 INVENTOR A4 EXfi/VDEI? F03 raw/04 2 KARL, BAT/I ATTORNEY THREE-ELEMENT ELECTRON DISCHARGE TUBE The present invention relates to high-vacuum electron tubes, more particularly to tubes of the type including an anode, a cathode and a control electrode and means to produce a magnetic field acting on the electron stream emitted from the cathode, to reduce the number of electrons reaching the control electrode, especially where the latter is biased at a positive potential relative to the cathode, whereby to in turn reduce the power necessary to control or drive the tube.

As is well known, in connection with certain specific operations of high-vacuum electron tubes of conventional construction, appreciable power losses may occur in the grid or control circuit of a tube, such as in the case of the end or power stage of a transmitting amplifier. In order to achieve a required output power, it is no longer practical or possible to operate a tube with negative grid bias or control potential, as used for pure voltage amplification, but rather to bias and drive the control electrode to high positive potentials according to what is commonly known as class-C operation of an electron tube.

In the attempt to reduce the control power resulting from a positive potential upon the control electrode, there has already been proposed a tube construction including a plurality of incandescent filamentary cathodes or wires each extending parallel to and between adjacent wires of a control or grid electrode. A permanent magnet associated with the tube serves to produce a magnetic field in the main direction of the electron stream, whereby to cause the electrons emitted by said cathode wires and accelerated towards the anode to follow a spiral path having a diameter of a sufficiently-small value, by the magnetic field having a sufficiently high value, such as to cause practically all the electrodes emitted by said cathodes (about 97 percent to 98 percent) to pass through the interstices between the grid wires on their way to the anode, even with relatively high positive grid-operating potentials. For further details concerning this type of tube, reference is made to articles by J .A. Darmer, Cathode Press 20, 1965, No. 2, page 22, and by H. Langer, page 31 of the same issue.

A disadvantage, among others, of a tube described in the foregoing is the fact that, due to the relatively great spacing distance between grid wires, the effect of the anode potential on the electric field strength in the vicinity of the cathode is relatively high, resulting thereby in a relatively low amplification factor of the tube. Besides, the increase of the electron transit paths resulting from the spiral electron flow, entails the further disadvantage of decreasing the output power of the tube, especially at higher operating frequencies.

Accordingly, an important object of the present invention is the provision of an improved electron tube construction, especially suitable as a power amplifier operated at positive grid or control potential (class-C operation), by which the foregoing and related difficulties and drawbacks are substantially overcome or minimized.

A more specific object of the invention is the provision of a high'vacuum electron tube amplifier, having a cathode anode and control electrode, said amplifier including means to provide a magnetic deflecting field causing practically all the electrons emitted by the cathode to follow a curved discharge path'towards the anode, substantially without any of the electrons reaching the control electrode even with the latter being at its highest positive operating potential.

The invention, both as to the foregoing and ancillary objects as well as novel aspects thereof, will be better understood from the following detailed description of a preferred embodiment of the invention, taken in conjunctionwith the accompanying drawings forming part of this specification and in which:

FIG. 1 is a longitudinal cross-sectional view through an electron tube constructed in accordance with the principles of the invention;

FIG. 2 is a transverse section view taken on line'2-2 of F l6. 1;

FIG. 3 is a cross-sectional view similar to FIG. 2, showing a modification of the invention; and

FIG. 4, is a fragmentary view ofthe embodiment of FIGS. 1 and 2 and showing a feature of improvement of the invention.

Like reference numerals denote like parts in the different views of the drawings.

With the foregoing objects in view, the invention, according to one of the aspects thereof, involves generally the provision of a high-vacuum three-electrode electron tube comprising essentially a central elongated control electrode, an anode having at least one oblong anode surface spaced from and extending in a direction parallel to the axis of said control electrode, and an oblong or wire-shaped cathode juxtaposed and extending along and in aligned relation to said anode surface. A magnet, preferably in the form of a solenoid or electromagnet, serves to produce a magnetic field within the space enclosed by said control electrode and anode surface in a direction parallel to the lengthwise dimension of said electrodes, or at right angle to the electron flow from said cathode to said anode surface. The magnetic field strength has a sufficiently high value, by adjusting the magnetizing current of the solenoid to a proper intensity, whereby to deflect or bend the electron stream emitted by the cathode into a curved path in the direction towards the anode surface and to reduce the number of electrons reaching the control electrode to a minimum, even with the latter being at a relatively high positive potential during operation.

In order to obtain a desired ratio of the effects of the control electrode and anode, respectively, on the electric field strength in the vicinity of the cathode, or to provide a predetermined amplification factor of the tube, electrostatic focusing electrode or shielding means, in the form of a shielding plate or the like disposed between the cathode and anode surface, are provided, said electrode projecting into the space between said control electrode and anode to an extent, to result in the desired electric field strength ratio at the cathode. originating from predetermined potential changes upon the control and anode electrodes, respectively, corresponding to a desired amplification factor of the tube. According to an especially advantageous and practical tube construction, to increase the total output power of the tube, a plurality of segmental anode surfaces, forming part of a cylindrical anode, are arranged concentric with and about a cylindrical control electrode with separate cathode wires and associated shielding plates being disposed in the spaces between adjacent anode surfaces, in the manner as will become more apparent as the description proceeds in reference to the drawings.

Referring more particularly to FIGS. 1 and 2, the electron tube shown comprises a central control electrode 1 of circular hollow-cylindrical cross section connected, via an insulating glass ring 2, to the base or mount support 3 of the tube. Disposed concentrically with the control electrode 1 there is a hollow cylindrical anode 4 being closed at its bottom 5 and likewise connected, via a glass insulating ring 6, to the base 3. The anode cylinder 4 is provided, in the example shown, on its inside surface with a plurality of axial grooves or recesses 7 which subdivide the circular cylindrical internal anode surface into a plurality of angularly spaced segmental partial anode surfaces 8, an incadescent cathode in the form of an axially tensioned cathode wire 9 being arranged inside each recess 7.

A mounting frame, comprised of a number of spaced mounting plates l014 interconnected by spacing rods, 15- 17, is supported by the base 3 and serves to in turn support the cathode wires or filaments 9. This frame carries, at its lower end, a cathode plate 19 supported by way of ceramic insulators 18 and, at its upper end, a number of cathode connector rods 22 displaceably mounted in insulating bushes 20 and 21 in the plates 11 and 10, respectively. The cathode wires 9, being secured, at one end, to the cathode supporting plate 19 and, at its opposite end, to an associated cathode supporting rod 22, are held under axial tension by means of compression springs 23 engaging the upper end of the rods 22, on the on hand, and the bushes 20, on the other hand.

The cathode supporting rods 22 are alternatively joined, via flexible connecting leads 24, to one of a pair of cathode supporting rings 25 and 26, respectively. The latter are in turn supported by cathode connector pins or prongs 27 and 28, mounted upon the base 3 through glass rings 29 and 30 and serving as external cathode terminals of the tube, it being understood that the pins 28 are insulatingly passed through the base 3 of the tube. Each cathode wire 9 is surrounded by a screening or focusing electrode 31 of U-shaped cross section, in the example shown. Each of the units 31 is secured to one of the spacing rods 16, whereby to assume the potential of the base or mounting support 3.

The legs of the focusing electrode 31 constitute plateshaped shielding or screening electrodes each arranged between a cathode wire 9 and an adjacent partial anode surface 8, said electrodes extending substantially in a direction parallel to the electric field, resulting from the potential upon the control electrode 1, and projecting into the space between the control electrode 1 and the anode surfaces 8 to an extent A, FIG. 2, such that, with no current flowing through the tube, the ratio of the electric field strength E, in the vicinity of the cathodes 9 resulting from unit control voltage upon the control electrode 1 to the field strength E, in the vicinity of said cathodes resulting from unit anode voltage in substantially equal to the desired amplification factor of the tube. In other words, the electrons emitted by the filaments 9 are initially focused towards the control electrode 1, to result, in cooperation with the magnetic field, in the cycloidal paths C towards the anode surfaces 8 substantially bypassing said control electrode.

With the electrode configuration shown and described in the foregoing being otherwise identical, the field strengths E, and E and, in turn, the amplification factor, are a function of the depth A of penetration of the shielding electrodes 31 into the space enclosed by the control and anode electrodes of the tube. The desired field strengths as a function of parameter A follow from the known Laplace equation for given values of the boundary potentials and parameter A.

A solenoid coil 40 in which the anode cylinder 4 is arranged concentrically serves to produce a magnetic field in a direction parallel to the axis of the tube, or at right angle to the direction of the electron streams emitted by the cathodes 9 and the adjacent anode surfaces 8. The tube may be cooled in a known manner by the use of a suitable coolant, for example water, circulated through the annular gap between the solenoid 40 and the anode cylinder 4, the latter being advantageously provided with cooling fins (not shown), to improve the cooling effect, in a manner well known to those skilled in the art.

In the following will be described the operation of the tube shown by FIGS. 1 and 2. Because of the magnetic field, the electrons emitted by the cathodes 9 move along curved cycloid-shaped paths, as indicated at B in FIG. 2, whereby to impinge upon or reach the adjacent anode surfaces 8. With the magnetic field strength having a sufficiently high value, obtained by adjustment of the solenoid current to a proper value, substantially no electrons reach the control electrode 1 even with the latter being at its maximum positive operating potential. As a consequence, no appreciable current flow occurs through the control circuit, resulting thereby in a minimum power required to drive or operate the tube. With no input signal applied to the tube, little or no anode current then flows at zero control voltage because of the strong space charge in the vicinity of the cathodes 9 and because of the high amplification factor or low relative effectiveness of the anode voltage in producing an electric field at the cathodes. Adjustment of the potential upon the shielding electrodes 31 to a negative or slightly positive value, relative to ground or other reference potential point of the circuit in which the tube is connected, can reduce the anode current to zero at zero control voltage, in accordance with the displacement of the family of characteristic curves of the tube.

Besides minimizing or preventing power losses in the control circuit, the invention has the further advantage, due to the removal of the grid of control electrode from the discharge space between the cathode and the anode, of enabling the spacing distance between the cathodes and anode to be reduced, compared with conventional electrode arrange ments, whereby to in turn reduce the electron transit time and to increase the maximum admissible operating frequency of the tube.

The U-shaped shielding units or electrodes 31 used in the tube according to FIGS. 1 and 2 cause the control voltage to draw off considerably more electrons from the side of the cathode wires 9 facing the open end or aperture of the U than from the side remote from said aperture. This has the effect that considerably less use can be made of the electron emission of the cathodes from the latter side, or side remote from the apertures, than from the sides facing the apertures of the units 31.

Improved use is made of the electron emission of the cathodes 9 by a modified tube construction shown in FIG. 3. The tube according to this variant of the invention is of annular cross section comprising two concentric control electrodes 32 and 33 having circular cylindrical surfaces 34 and 35 facing one another and between which there is disposed the anode in the shape of a circular cylindrical member provided with a series of radial slots, to result in a plurality of segmental partial anodes 36, each of the slots 37 containing a cathode wire 9 and two radial shielding plates 38, one on each side of said cathode wires. In an arrangement of this type, approximately half of the number of electrons emitted by the cathodes 9 are accelerated in opposite directions towards each of the control electrodes 33 and 34 along a pair of cycloid-shaped paths, as indicated at C in FIG. 3. Cooling ducts 39 may be provided in the anode member for the purpose ofcooling the tube.

According to a further feature of improvement of the invention, auxiliary grid-shaped control electrodes may be provided in the tube described in the foregoing between each of the cathodes 9 and the anode surfaces 8, to provide a four-element electron tube or tetrode in place of the triode shown in the drawings.

An arrangement of the latter type is shown, by way of example, in FIG. 4 in the form of an auxiliary control electrode or grid disposed within the shielding units 31, said auxiliary grid being comprised of two axial rods 40 linked by a plurality of ridge bars or wires 41, to form a ladder-shaped grid or electrode.

In the foregoing the invention has been described in reference to a specific illustrative or exemplary device. It will be evident, however, that variations and modifications, as well as the substitution of equivalent parts or elements for those shown herein for illustration, may be made without departing from the broader scope and spirit of the invention as set forth in the appended claims. The specification and drawing are accordingly to be regarded in an illustrative rather than in a restrictive sense.

I claim:

1. An electron discharge tube comprising in combination:

1. a central rod-shaped control electrode;

2. an anode electrode having a plurality of mutually spaced anode surfaces concentric with the axis of and surrounding said control electrode;

3. a cathode electrode comprising a plurality of incandescent filaments each disposed between adjacent anode surfaces and extending parallel to the axis of said control electrode;

4. means to produce a magnetic field within the space between said control and anode electrodes having a direction parallel to said axis; and

5. a plurality of focusing electrodes intervening between each of said filaments and the adjacent anode surfaces and projecting towards said control electrode to an extent such as to cause, in cooperation with said magnetic field, the electron discharge streams to pass from said filaments to the adjacent anodes along curved paths while substantially bypassing said control electrode.

2. An electron discharge tube as claimed in claim 1, said control electrode having a circular cross section and said anode electrode consisting of a hollow cylinder concentric with said control electrode and provided upon its inside surface with a plurality of spaced radial recesses extending parallel to the axis of said control electrode and said filaments and focusing electrodes being disposed within said recesses.

' 3. An electron discharge tube as claimed in claim I, said control electrode having a circular cross section and said anode electrode consisting of a hollow cylinder concentric with said control electrode and provided upon its inside surface with a plurality of spaced radial recesses extending parallel to the axis of said control electrode, said filaments being disposed within said recesses, and said focusing electrodes consisting of oblong U-shaped separating elements enclosing said filaments with their legs projecting into the space between said control and anode electrodes.

4. An electron discharge tube as claimed in claim 1, said control electrode having a circular cross section and said anode electrode consisting of a hollow cylinder concentric with said control electrode and provided upon its inside surface with a plurality of spaced radial recesses parallel to the axis of said control electrode, said filaments being disposed within said recesses and said focusing electrodes consisting of oblong U-shaped separating elements enclosing said filaments with their legs projecting into this space between said control and anode electrodes, and a plurality of'screen grid electrodes each disposed within one of said separating elements adjacent to the open ends thereof.

5. An electron discharge tube as claimed in claim 1, said control electrode having a circular cross section and said anode electrode including a plurality of circularly arranged and angularly spaced segmental elements forming an anode assembly concentric with said control electrode, said fila ments being disposed within the spaces between adjacent segmental elements, and said focusing electrodes consisting of pairs of parallel plates disposed radially on the opposite sides of the respective filaments, and a further cylindrical control electrode spaced outwardly from said anode and concentric with said first control electrode.

6. An electron discharge tube as claimed in claim I. said control electrode having a circular cross section. said anode surfaces coinciding with a cylinder concentric with said control electrode, and said magnetic filed producing means consisting of a magnet coil surrounding said anode electrode concentric therewith and said control electrode 7. An electron discharge tube comprising in combination:

I. an elongated control electrode;

2. an anode having at least one elongated anode surface spaced from and arranged parallel to said control electrode;

3. an elongated filamentary cathode in juxtaposed and aligned relation to said anode surface;

4. means to produce a magnetic field in the space between said control electrode and said anode surface having a direction parallel to the axis of said control electrode; and

5. focusing means to initially direct the electron stream emitted by said cathode towards said control electrode;

6. said magnetic field having an intensity to cause, in cooperation with said focusing means, the electron stream emitted by said cathode to follow a curved path towards said anode surface while substantially bypassing said control electrode.

8. An electron discharge tube as claimed in claim 7, said focusing means designed to cause the electric field strength at said cathode resulting from a predetermined potential change upon said control electrode to be a desired multiple of the electric field strength at said cathode resulting from the same predetermined potential change upon said anode.

9. An electron discharge tube as claimed in claim 8, said focusing means being comprised of a U-shaped electrostatic shield surrounding said cathode and projecting towards said control electrode to an extent as to cause the electric field strength at said cathode resulting from a predetermined potential change upon said control electrode to be a desired multiple of the electric field strength at said cathode resulting from the same predetermined potential change upon said anode. 

1. An electron discharge tube comprising in combination:
 1. a central rod-shaped control electrode;
 2. an anode electrode having a plurality of mutually spaced anode surfaces concentric with the axis of and surrounding said control electrode;
 3. a cathode electrode comprising a plurality of incandescent filaments each disposed between adjacent anode surfaces and extending parallel to the axis of said control electrode;
 4. means to produce a magnetic field within the space between said control and anode electrodes having a direction parallel to said axis; and
 5. a plurality of focusing electrodes intervening between each of said filaments and the adjacent anode surfaces and projecting towards said control electrode to an extent such as to cause, in cooperation with said magnetic field, the electron discharge streams to pass from said filaments to the adjacent anodes along curved paths while substantially bypassing said control electrode.
 2. an anode electrode having a plurality of mutually spaced anode surfaces concentric with the axis of and surrounding said control electrode;
 2. An electron discharge tube as claimed in claim 1, said control electrode having a circular cross section and said anode electrode consisting of a hollow cylinder concentric with said control electrode and provided upon its inside surface with a plurality of spaced radial recesses extending parallel to the axis of said control electrode, and said filaments and focusing electrodes being disposed within said recesses.
 2. an anode having at least one elongated anode surface spaced from and arranged parallel to said control electrode;
 3. an elongated filamentary cathode in juxtaposed and aligned relation to said anode surface;
 3. An electron discharge tube as claimed in claim 1, said control electrode having a circular cross section and said anode electrode consisting of a hollow cylinder concentric with said control electrode and provided upon its inside surface with a plurality of spaced radial recesses extending parallel to the axis of said control electrode, said filaments being disposed within said recesses, and said focusing electrodes consisting of oblong U-shaped separating elements enclosing said filaments with their legs projecting into the space between said control and anode electrodes.
 3. a cathode electrode comprising a plurality of incandescent filaments each disposed between adjacent anode surfaces and extending parallel to the axis of said control electrode;
 4. means to produce a magnetic field within the space between said control and anode electrodes having a direction parallel to said axis; and
 4. An electron discharge tube as claimed In claim 1, said control electrode having a circular cross section and said anode electrode consisting of a hollow cylinder concentric with said control electrode and provided upon its inside surface with a plurality of spaced radial recesses parallel to the axis of said control electrode, said filaments being disposed within said recesses and said focusing electrodes consisting of oblong U-shaped separating elements enclosing said filaments with their legs projecting into the space between said control and anode electrodes, and a plurality of screen grid electrodes each disposed within one of said separating elements adjacent to the open ends thereof.
 4. means to produce a magnetic field in the space between said control electrode and said anode surface having a direction parallel to the axis of said control electrode; and
 5. focusing means to initially direct the electron stream emitted by said cathode towards said control electrode;
 5. An electron discharge tube as claimed in claim 1, said control electrode having a circular cross section and said anode electrode including a plurality of circularly arranged and angularly spaced segmental elements forming an anode assembly concentric with said control electrode, said filaments being disposed within the spaces between adjacent segmental elements, and said focusing electrodes consisting of pairs of parallel plates disposed radially on the opposite sides of the respective filaments, and a further cylindrical control electrode spaced outwardly from said anode and concentric with said first control electrode.
 5. a plurality of focusing electrodes intervening between each of said filaments and the adjacent anode surfaces and projecting towards said control electrode to an extent such as to cause, in cooperation with said magnetic field, the electron discharge streams to pass from said filaments to the adjacent anodes along curved paths while substantially bypassing said control electrode.
 6. An electron discharge tube as claimed in claim 1, said control electrode having a circular cross section, said anode surfaces coinciding with a cylinder concentric with said control electrode, and said magnetic filed producing means consisting of a magnet coil surrounding said anode electrode concentric therewith and said control electrode.
 6. said magnetic field having an intensity to cause, in cooperation with said focusing means, the electron stream emitted by said cathode to follow a curved path towards said anode surface while substantially bypassing said control electrode.
 7. An electron discharge tube comprising in combination:
 8. An electron discharge tube as claimed in claim 7, said focusing means designed to cause the electric field strength at said cathode resulting from a predetermined potential change upon said control electrode to be a desired multiple of the electric field strength at said cathode resulting from the same predetermined potential change upon said anode.
 9. An electron discharge tube as claimed in claim 8, said focusing means being comprised of a U-shaped electrostatic shield surrounding said cathode and projecting towards said control electrode to an extent as to cause the electric field strength at said cathode resulting from a predetermined potential change upon said control electrode to be a desired multiple of the electric field strength at said cathode resulting from the same predetermined potential change upon said anode. 